The present invention relates to an ultrasonic echo sounding device for the observation of the web formation and/or pulp suspension flow on the wire part in the head box of a paper machine. More particularly, the invention relates to a device having a series of ultrasonic detectors connected to the wall of the flow channel in the head box and/or to the forming wire or wires. The detectors direct an ultrasonic field at the pulp suspension and the echo signals received from the pulp suspension are detected.
Known prior art devices measure the thickness of a pulp layer placed on the wire in the wire part of a paper machine by an ultrasonic echo method. This is accomplished by placing a detector crystal beneath the wire, whereas the water film at the bottom surface of the wire acts as the generator of the acoustic contact. This prior art techinque is disclosed in Finnish Pat. Nos. 35,621 and 35,622 of the present inventor.
Acoustic microscopes based on so-called acoustic lenses are known in the prior art. The construction and principle of operation of such microscopes are described in a paper in Scientific American, Oct. 1979, entitled "The Acoustic Microscope", by Calvin F. Quate, pages 58 to 65.